Как сделать форму публикации записей как во вк?

<div id="input_block">
        <div class="contenteditable" contenteditable="true"></div>
        <div class="bottom_block">
            <input class="buttons submit" type="submit" name="submit" value="Отправить">
        </div>
    </div>

#input_block {
    display: block;
    position: relative;
    margin: 10px;
    width: 527px;
    height: auto;
    min-height: 143px;
    background-color: black;
}

.contenteditable {
    position: absolute;
    vertical-align: top;
    margin: 10px 10px 0px 10px;
    padding: 14px 12px 16px 12px;
    resize: vertical;
    width: 507px;
    height: auto;
    word-wrap: break-word;
    overflow: hidden;
    min-height: 72px;
    border: 1px solid orange; /*#e3e4e8*/
    /*border-bottom: none;*/
    border-top-left-radius: 2px;
    border-top-right-radius: 2px;

    color: red;
    background-color: white;
}

.bottom_block {
    display: block;
    position: absolute;
    box-sizing: unset;
    width: 507px;
    height: 50px;
    right: 0;
    bottom: 10px;
    margin-right: 10px;
    background-color: #fafbfc;
    border-top: 1px solid #e7e8ec;
    border-bottom-left-radius: 2px;
    border-bottom-right-radius: 2px;
}

.submit {
    position: absolute;
    margin: 10px;
    right: 0;
    bottom: 0;
}

/* Стиль для кнопок */
.buttons {
    font-family: 'PT Sans', sans-serif;
    font-size: 14px;
    text-transform: uppercase;
    color: white;
    /*line-height: 44px;*/
    padding: 5px 20px;
    background: black;
    letter-spacing: 0.1em;
    white-space: nowrap;
}

.buttons, .buttons:active, .buttons:focus {
    outline: none;
    border: none;
    cursor: pointer;
}

<div id="input_block">
    <div class="contenteditable" contenteditable="true" placeholder="Добавить запись..."></div>
    <div class="bottom_block">
        <input class="buttons submit" type="submit" name="submit" value="Отправить">
    </div>
</div>

#input_block {
    display: block;
    position: relative;
    width: 527px;
    min-height: 143px;
    margin: 10px;
    padding: 10px;
    background-color: black;
}

.contenteditable {
    vertical-align: top;
    width: 507px;
    min-height: 72px;
    margin: 0 auto;
    padding: 14px 12px 16px 12px;
    word-wrap: break-word;
    overflow: hidden;
    color: black;
    background-color: white;
    border: 1px solid #e3e4e8;
    border-bottom: none;
    border-top-left-radius: 2px;
    border-top-right-radius: 2px;
}

/* placeholder для div contenteditable */
[contenteditable=true]:empty:before{
    content: attr(placeholder);
    color: #828282;
    display: block; /* For Firefox */
}

/* placeholder меняет цвет при получении фокуса*/
[contenteditable=true]:focus:empty:before{
    content: attr(placeholder);
    color: #b8b8bb;
    display: block; /* For Firefox */
}

.bottom_block {
    display: block;
    box-sizing: unset;
    min-width: 507px;
    height: 50px;
    margin: 0 auto;
    right: 0;
    bottom: 10px;
    background-color: #fafbfc;
    border-top: 1px solid #e7e8ec;
    border-bottom-left-radius: 2px;
    border-bottom-right-radius: 2px;
}

.submit {
    position: absolute;
    margin: 10px 20px 10px 10px;
    right: 0;
    border-radius: 4px;
}

/* Стиль для кнопок */
.buttons {
    font-family: 'PT Sans', sans-serif;
    font-size: 14px;
    text-transform: uppercase;
    color: white;
    /*line-height: 44px;*/
    padding: 5px 20px;
    background: black;
    letter-spacing: 0.1em;
    white-space: nowrap;
}

.buttons, .buttons:active, .buttons:focus {
    outline: none;
    border: none;
    cursor: pointer;
}