Ridimensionamento automatico div contenitore

[chaskito]

Ridimensionamento automatico div contenitore

Buona sera a tutti.

Ho un problemino con il div contenitore (dissolve) ho definito un max-height e min-height resta sempre in 400px non riesco a far ridimensionare questo div. il div item (div delle immagini funziona tranquillamente si autoridimensiona).
non so dove sbaglio, qui di seguito ho il codice completo.

Un saluto

[HTML]<style>
/* dissolve */
.dissolve {position: relative;
overflow :hidden;
background-color:#ff0000;
width: auto;
max-height:1250px!important;
min-height:400px!important;
}
.dissolve .item {position: absolute;
display: block;
max-width:100%;
max-height:1250px;
min-height:100px;
width: auto;
height: auto;

margin-left:auto ;
margin-right:auto ;
opacity: 0;
-webkit-animation: dissolve 20s linear infinite;
-moz-animation: dissolve 20s linear infinite;
-ms-animation: dissolve 20s linear infinite;
animation: dissolve 20s linear infinite}
.dissolve .item:nth-child(2) {
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
-webkit-animation-delay: 5s;
-moz-animation-delay: 5s;
-ms-animation-delay: 5s;
animation-delay: 5s}
.dissolve .item:nth-child(3) {-webkit-animation-delay: 10s;
-moz-animation-delay: 10s;
-ms-animation-delay: 10s;
animation-delay: 10s}
.dissolve .item:nth-child(4) {-webkit-animation-delay: 15s;
-moz-animation-delay: 15s;
-ms-animation-delay: 15s;
animation-delay: 15s}

@-webkit-keyframes dissolve {0%, 30%, 100% {opacity: 0}
5%, 25% {opacity: 1}}
@-moz-keyframes dissolve {0%, 30%, 100% {opacity: 0}
5%, 25% {opacity: 1}}
@-ms-keyframes dissolve {0%, 30%, 100% {opacity: 0}
5%, 25% {opacity: 1}}
@keyframes dissolve {0%, 30%, 100% {opacity: 0}
5%, 25% {opacity: 1}}

</style>
<div class="dissolve">
<img class="item" src="slider/001.jpg"/>
<img class="item" src="slider/002.jpg"/>
<img class="item" src="slider/003.jpg"/>
<img class="item" src="slider/004.jpg"/>
</div>[/HTML]